Aligning bone's roll accurately to rotated objects
Riggers usually set the bone roll to have the main movements on the X axis (like in your example, possibly having the main rotation with positive values of X). But if you simply parent the external bones to the central, all 3 bones will rotate on the central bone X axis, which is not what you want. One good approach could be setting two drivers, so that every rotation of the central bone will be reflected by the external bones (on their own axis).